<!DOCTYPE html>
<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#scroll-timeline-at-rule">
<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#phase-algorithm">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/web-animations/testcommon.js"></script>
<style>
  #scroller {
    overflow: scroll;
    width: 100px;
    height: 100px;
  }
  #contents {
    height: 200px;
  }
  @keyframes expand {
    from { width: 100px; }
    to { width: 200px; }
  }
  #element {
    width: 0px;
  }
  /* Ensure stable expectations if feature is not supported */
  @supports not (animation-timeline:foo) {
    #element { animation-play-state: paused; }
  }
</style>
<div id=scroller>
  <div id=contents></div>
</div>
<div id=container></div>
<script>
  promise_test(async (t) => {
    try {
      // Make sure scroller has a layout box.
      await waitForNextFrame();

      container.innerHTML = `
        <div id=element></div>
        <style>
          @scroll-timeline timeline {
            source: selector(#scroller);
            time-range: 10s;
            start: 50px;
            end: 100px;
          }
          #element {
            animation: expand 10s linear;
            animation-timeline: timeline;
          }
        </style>
      `;
      // Animation should not apply in before phase.
      assert_equals(getComputedStyle(element).width, '0px');
      await waitForNextFrame();
      // Animation should still not apply.
      assert_equals(getComputedStyle(element).width, '0px');
    } finally {
      container.innerHTML = '';
    }
  }, 'Animation does not apply when timeline phase is before');
</script>
